Fiber optic splice closure

ABSTRACT

A fiber optic splice closure includes a series of stacked splice trays pivotally secured within a housing, and oval shaped generally flexible transport tubes carrying the exposed optical fibers to the splice trays within the closure. The transport tubes have a differential flexibility to permit bending i a direction generally normal to the major dimension of the tube while preventing bending in a direction generally normal to the minor dimension of the tube. Accordingly, optical fiber ribbons carried by the transport tubes are protected from bending in a direction normal to their minor dimension. The splice trays are pivotally secured at one end to a bracket secured to an end cap of the housing. A hinge for each splice tray includes detents to hold an individual tray in a raised position to thereby facilitate access to an underlying tray. In addition, splice holders are provided on each splice tray and include a series of generally flexible walls extending outwardly from a base. The flexible walls further include hollow cavities to more readily accommodate splices of different sizes. A generally rigid shell with a predetermined pattern of openings therein is positioned to overlie the base carrying the flexible walls.

FIELD OF THE INVENTION

The present invention relates to the field of fiber optics and, moreparticularly, to a fiber optic splice closure including stacked spliceorganizing trays, splice holders, and transport tubes carrying opticalfibers to the splice trays.

BACKGROUND OF THE INVENTION

Optical fiber communications systems, employing fiber optic cables anddigital electronics, are widely used in the telecommunication industryto transmit large volumes of data and voice signals over relatively longunrepeatered distances, and virtually noise free. Splice points and droppoints for the fiber optic cables are required for most such systems. Ata splice point, for example, all of the fibers at one end of a cable arespliced to corresponding fibers of a tandem cable. At a drop point orexpress splice point, some of the fibers may be spliced to a drop cable,while most of the fibers are passed through the drop point unaltered.

For both splice points and drop points, the optical fibers are exposedfrom the protective cable jacket to be spliced and secured within asplice closure. The splice closure typically includes a protectivehousing with either a single end cap through which cables penetrate,that is, a butt-splice; or dual opposing end caps through whichrespective cables penetrate, that is, an in-line splice.

A typical butt-splice closure, such as the model FOSC 100 made by theassignee of the present invention, typically includes one or more spliceorganizers, or splice trays, disposed in stacked arrangement within theprotective housing. The trays are pivotally connected at one end to amounting bracket which, in turn, is connected to the inside face of theclosure end cap. The pivotal connection permits individual splice traysto be temporarily moved to a raised position by the insertion of aremovable spacer or clip near the pivot point. Accordingly, access isthen available to the underlying splice tray, such as to check fiberrouting or to remake a defective splice.

The cables extending into the housing are secured therein and thepenetration point sealed to prevent water from entering the protectivehousing. Since the protective cable sheath is removed within thehousing, flexible protective tubes, known as "transport tubes" are usedto protect predetermined groupings of the optical fibers extending fromthe cable securing point to respective splice organizer trays. Suchconventional transport tubes typically have a circular cross-section anda uniform wall thickness. For a typical fiber optic cable of theloose-buffer type, the predetermined groupings are typically all thosefibers within a given buffer tube. In other words, a transport tubeslides over an end portion of a respective buffer tube to carry andprotect the fibers extending to the splice tray. One or more suchtransport tubes are routed to and secured to each splice tray.

The transport tubes must protect the optical fibers despite any bendingthat occurs, such as when the splice trays are pivoted to the raisedposition to access an underlying tray. Moreover, the transport tubesmust prevent the optical fibers from bending more sharply than theminimum bend radius. Since individual fibers extend through thetransport tubes when using a loose buffered cable, these individualfibers may readily bend along with the transport tube.

For many applications, higher fiber count cables are required. Higherfiber count cables having a relatively small cable cross-section areavailable and include a plurality of optical fiber ribbons, such asLIGHTPACK® fiber optic cables offered by AT&T. Optical fiber ribbons maybe readily bent only in a direction normal to their major dimensionequivalently to the minimum bend radius of the individual fibers.However, the ribbons may not be bent as sharply in the direction normalto their minor dimension. In other words, optical fiber ribbonspreferentially bend only in the direction normal to their majordimension. Moreover, the ribbons should not be bent in the direction oftheir minor dimension or high signal attenuation or physical damage mayresult.

Unfortunately, optical fiber ribbons positioned within a conventionaltransport tube may be bent in any direction thereby increasingattenuation and possibly physically damaging the ribbons. In addition, aconventional transport tube also permits an optical fiber ribbon to bedeformed from its flat shape and compressed or buckled when a tie wrap,for example, is used to secure the end of the transport tube to a spliceorganizer tray. Accordingly, a conventional circular cross-sectionaltransport tube is unacceptable for use in a splice closure for ribbonoptical fiber cables.

Also related to the quality and longevity of optical fiber splicessecured within a splice closure is a splice holder, several of which aretypically mounted on a splice tray. The splice holder retains theindividual splices between corresponding optical fibers. A typicalsplice holder may accommodate four to ten splices and must adequatelysecure the splices in the presence of mechanical shocks and vibration.The splices are typically protective sleeves for fusion-spliced fibers,or may be mechanical splices which position and maintain the opticalfiber ends in precise alignment. For example, U.S. Pat. No. 4,679,896 toKrafcik et al. discloses a typical splice holder formed of a resilientblock with a series of channels formed therein to closely resilientlyreceive optical fiber splices.

There is no industry standard for the precise external dimensions of anoptical fiber splice; rather, there are a number of popular commerciallyavailable mechanical and fusion splices, most with different exteriordimensions. AT&T in an attempt to accommodate a number of differenttypes of splices of different sizes, for example, offers a splice holderhaving a series of spaced apart deformable walls of a foam material toaccommodate different sized splices. In a similar fashion, U.S. Pat. No.4,793,681 to Barlow et al. discloses a splice holder with pairs ofopposing leaf springs to accommodate different sized splices. U.S. Pat.No. 4,854,661 to Cooper et al. discloses a lid over the splice holderwith a resilient pad positioned within the lid to hold the fiber spliceswithin respective shallow grooves of the underlying splice holder.Similarly the DeSanti patent, U.S. Pat. No. 4,687,289, includes a lidwhich may be offset from underlying grooves to thereby accommodate aslightly smaller fusion splice, as compared to a typical mechanicalsplice. Despite attempts to accommodate different sized splices therestill exists a need to do so while properly cushioning the splicesagainst mechanical shock and vibration.

A splice closure also typically includes a lower slack storage trayadjacent the stacked splice trays. The slack storage tray isparticularly important for a drop splice where a large number of fibersare passed through the splice closure without being spliced. A typicalslack storage tray is generally rectangular in shape withperpendicularly extending opposing sidewalls. The slack storage trayextends generally lengthwise within a cylindrical housing as in the FOSC100 splice closure. Unfortunately, such a storage tray has a limitedcapacity for slack storage because the height of its perpendicularlyextending sidewalls is limited by the size of the cylindrical housing.As higher fiber count cables are required, especially for drop orexpress splice points, additional slack storage capacity is needed.

Another concern relating to splice closures includes an ability topreferentially separate a desired optical fiber or ribbon from a slackbundle on a splice organizer tray with minimum disturbance to adjacentfibers. This tedious task is typically attempted by using a relativelysmall hooked probe, such as a crochet needle, to separate a desiredoptical fiber or ribbon from slack which is positioned adjacent sidewalls of the splice tray.

SUMMARY OF THE INVENTION

In view of the foregoing background, it is, therefore, an object of thepresent invention to provide a splice closure including transport tubesthat prevent undesired bending of ribbon type fiber optic cables andthat may also accommodate loose buffer tube cables.

It is another object of the invention to provide a fiber optic spliceclosure including a series of splice trays that may be arranged in astacked position or may be moved to a raised position to facilitateaccess to an underlying tray.

It is yet another object of the invention to provide a fiber opticsplice closure having a series of splice holders that can readilyaccommodate various splices having different external dimensions.

It is still another object of the invention to provide a fiber opticsplice closure including splice trays that permit the ready separationof predetermined fibers from adjacent slack fibers.

These and other objects, advantages and features of the presentinvention are provided by a fiber optic splice closure including ahousing, a plurality of splice trays positioned within the housing andpivotally connected therein, and a plurality of generally flexibletransport tubes extending from the fiber optic cable ends to the splicetrays for carrying optical fibers broken out and routed to respectivesplice trays, wherein each of the transport tubes includes means forimparting differential flexibility between first and second directionstransverse to the longitudinal axis of the transport tube. The means forimparting differential flexibility to the transport tube preferably isprovided by a predetermined cross-sectional shape of the transport tube.

Preferably the cross-sectional shape of each transport tube is generallyoval with a major dimension and a minor dimension to thereby impartgreater flexibility for bending in the direction normal to the majordimension. Accordingly, an optical fiber ribbon positioned within thetransport tube will preferably bend along its major dimension ratherthan its minor dimension. The transport tube also preferably has thickeropposing end wall portions than opposing side wall portions to impartthe desired differential flexibility.

As would be readily understood by those skilled in the art, thetransport tube preferably has a predetermined major interior dimensionfor receiving therein a fiber optic ribbon formed of a predeterminednumber of optical fibers arranged in side-by-side relation. The minorinterior dimension of the transport tube is also preferably selected tofrictionally engage any of a range of commercially available fiber opticloose buffer tubes. Accordingly, the transport tube may be used for bothoptical fiber ribbon cable and loose buffer tube cable.

The splice closure also preferably includes a bracket for pivotallymounting the splice trays. A hinge for each splice tray includes detentsfor holding a respective splice tray in either of two raised position tothereby facilitate access to an underlying splice tray. Access to anindividual splice tray may be desired to locate or remake a defectivesplice.

The splice closure also includes cable termination means for securingone or more optical fiber cables within the splice closure housing. Inaddition, the cable termination means preferably includes guide meansfor guiding optical fibers from the one or more optical fiber cablesalong a predetermined bend radius and to the transport tubes. The guidemeans may accommodate either optical fiber ribbons or individual opticalfibers.

The guide means preferably includes a base connected to the bracket thatmounts the splice trays. An arcuately shaped wall having thepredetermined bend radius extends outwardly from the base. Transporttube receiving means is provided for the guide means by a series ofspaced apart walls extending outwardly from the base of the guide meansand thereby defining a series of slots for securing the transport tubes.

Another aspect of the present invention is an enlarged capacity slackstorage tray positioned within the splice closure housing. Conventionalslack storage trays are generally rectangular in shape and thus have alimited height when positioned within a cylindrical housing. The slackstorage tray according to the present invention includes a portiondefined by a generally rectangular base and a pair of opposing sidewalls extending outwardly from the base at a predetermined obtuse anglegenerally following an adjacent curved portion of the cylindricalhousing. Accordingly, an additional volume of slack storage space isobtained. This additional slack storage capacity is especially importantfor an express or drop splice point where many of the fibers are notspliced, but rather simply pass through the splice closure and must bestored as slack.

One or more fiber optic splice holders are positioned on each splicetray positioned within the splice closure. Yet another feature of thepresent invention is a splice holder that can accommodate a range ofvarious manufacturers' splices that have different external dimensions.The splice holder according to the invention includes a base and aseries of spaced apart flexible walls extending outwardly from the baseand defining a series of channels between adjacent pairs of the walls.Moreover, each of the walls has a hollow cavity extending through asubstantial portion thereof and is formed of a flexible material tothereby readily accommodate splices of different sizes within respectivechannels. The base and walls of the splice holder are preferably formedof integrally molded rubber.

An embodiment of the splice holder preferably includes a pair of insertspositioned in spaced apart relation and wherein each insert includes abase and a series of upstanding walls. The inserts are preferablypositioned so that the walls extend through corresponding openings in agenerally rigid shell which overlies the bases and provides supportthereto. The shell also preferably has side walls to support theperipheral flexible walls and prevent them from bending outwardly.

Another feature of the present invention is that the bracket mountingthe splice trays is generally U-shaped. Accordingly, a cable may bereadily positioned passing through the U-shaped opening and to anopposite side of the splice closure. In many typical prior art spliceclosures, the bracket had a central opening which, therefore, requiredcarefully threading a substantial length of cable through the centralopening. The U-shaped bracket of the present invention overcomes thisshortcoming of the prior art splice closures.

Still another feature of the present invention is that the splice traysinclude at least one pair of spaced apart ridges on an inner portion ofopposing side walls of the splice tray. The ridges permit insertion of ahooked probe between the ridges to thereby facilitate separation of apredetermined optical fiber or group of optical fibers from adjacentslack optical fibers.

A method aspect according to the invention includes positioning over anoptical fiber ribbon a generally flexible transport tube as describedabove. The transport tube has a longitudinal axis and a predeterminedcross-sectional shape for imparting to the transport tube differentialflexibility between first and second directions transverse to thelongitudinal axis. The first direction corresponds to the directiongenerally normal to the major dimension of the optical fiber ribbon andhas a substantially greater flexibility than the second direction whichcorresponds to the direction generally normal to the minor dimension ofthe optical fiber ribbon.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cutaway perspective view of a splice closure according tothe invention.

FIG. 2 is a plan view of the splice closure according to the inventionwith the housing and end cap removed to illustrate the series of stackedsplice trays.

FIG. 3 is a side elevational view of the splice closure according to theinvention with the housing removed to illustrate the series of stackedsplice trays and the stack storage tray.

FIG. 4 is a plan view of the slack storage tray and fiber optic guide asin the splice closure according to the invention.

FIG. 5 is a cross-sectional view of the slack storage tray of FIG. 4taken along line 5--5.

FIG. 6 is a greatly enlarged cross-sectional view of the fiber opticguide as shown in FIG. 4 taken along line 6--6 and illustrating fiberoptic transport tubes secured to a portion of the guide.

FIG. 7 is a greatly enlarged cross-sectional view of a portion of anembodiment the fiber optic transport tube according to the invention.

FIG. 8 is a perspective view of a splice holder according to theinvention.

FIG. 9 is an exploded perspective view of the splice holder as shown inFIG. 8.

FIG. 10 is a bottom view of a corner portion of the splice holder asshown in FIG. 8.

FIG. 11 is a cross-sectional view of the splice holder as shown in FIG.8 taken along line 11--11.

FIG. 12 is a cross-sectional view of the splice holder as shown in FIG.8 taken along line 12--12.

FIG. 13 is a perspective view of a portion of the bracket and splicetray pivotally secured thereto according to the invention.

FIG. 14 is a greatly enlarged cross-sectional view taken along line13--13 of FIG. 13 showing the splice trays in a stacked position.

FIGS. 15 and 16 are cross-sectional views similar to FIG. 14 showing thesplice tray in a first and second raised position, respectively.

FIG. 17 is a greatly enlarged cross-sectional view taken along line17--17 of FIG. 13 illustrating the connection of a transport tube to thesplice tray.

FIG. 18 is a side elevational view of the hinge portion of the bracketand splice trays according to the invention illustrating the movement ofa splice tray to a fully raised position, such as to facilitate removalof a splice tray.

FIG. 19a is a perspective view of the friction fit connection betweenthe transport tube according to the invention and an optical fiber loosebuffer tube.

FIG. 19b is a cross-sectional view taken along line 19b--19b of FIG.19a.

FIG. 20a is a fragmentary perspective view of the transport tubeaccording to the invention in which an optical fiber ribbon ispositioned.

FIG. 20b is a cross-sectional view taken along line 20b--20b of FIG.20a.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, applicants provide theseembodiments so that this disclosure will be thorough and complete, andwill fully convey the scope of the invention to those skilled in theart. Like numbers refer to like elements throughout.

A fiber optic splice closure according to the invention is generallydesignated as 30 in the accompanying drawings. The illustratedembodiment of the splice closure 30 is for a butt-splice, although, aswould be readily understood by those skilled in the art, the features ofthe present invention may also be similarly and beneficially applied toan in-line splice.

Referring now to FIGS. 1-3, several components of the splice closure 30according to the invention will be described for general orientation.The splice closure 30 includes a generally cylindrical housing 31 withan end cap 32 secured thereto. One or more fiber optic cables 33 enterthe housing 31 through suitable openings in the end cap 32. The cables33 are secured within the splice closure 30 by cable termination means,such as including the use of conventional strain relief clamps asdescribed below.

A series of splice trays 35 is pivotally connected at one end to amounting bracket 37 which, in turn is connected to an inside face of theend cap 32. Each of the splice trays 35 preferably includes a series ofsplice holders 36 as more fully described below. The individual splicetrays 35 are movable between a stacked position and a raised position tofacilitate access to an underlying splice tray 35 (FIG. 3) also as morefully described below.

The optical fibers from the optical fiber cables 33 are carried byflexible transport tubes 40 to respective splice trays 35. The transporttubes 40 must be sufficiently flexible to permit the splice trays 35 tobe moved between the stacked and raised positions, yet still besufficiently rigid to prevent more sharply bending the optical fibersthan the desired minimum bend radius.

The transport tube 40 according to the present invention includes meansfor imparting to the tube differential flexibility between first andsecond directions transverse to a longitudinal axis of the tube.Preferably the means for imparting the differential flexibility is apredetermined cross-sectional shape of the tube. A generally ovalcross-sectional shape, as discussed in greater detail below, providesthe differential flexibility. Accordingly, when the transport tube 40according to the invention is used to carry one or more optical fiberribbons, the ribbons are prevented from bending in a directiontransverse to the minor dimension of the optical fiber ribbon, and,instead bend preferentially in a direction transverse to the majordimension of the ribbon.

Another feature of the present invention as illustrated best in the planview of FIG. 2, is the provision of pairs of spaced apart ridges 39extending from opposing side walls 35b of each splice tray 35. As shownin the illustrated embodiment, the splice tray 35 includes a generallyrectangular base 35a and a pair of opposing side walls 35b extendingoutwardly therefrom. The ridges 39 on the side walls 35b permit atechnician to insert a hooked probed therebetween to engage and separateout predetermined fibers from adjacent slack fibers 50.

Referring now to FIGS. 3-6, several features of the present inventionare best understood. The mounting bracket 37 is generally U-shaped witha first leg secured to an inner face of the end cap 32. The generallyU-shaped mounting bracket 37 provides a U-shaped or slotted opening 38to permit a fiber cable to be routed through the opening to an oppositeside of the splice closure 30. In other words, the U-shaped mountingbracket 37 according to the invention permits even a substantial lengthof slack cable to be routed to an opposite side of the splice closure.Thus, the U-shaped mounting bracket 37 overcomes a shortcoming of theprior art which provided a bracket having a central opening and throughwhich the a substantial length of cable would have to carefullythreaded.

The splice closure 30 also includes a slack storage tray 45 connected atone end to the U-shaped mounting bracket 37 and positioned below theseries of splice trays 35. The slack storage tray 45 includes agenerally rectangular base 46 and pair of opposing side walls 47extending outwardly at an obtuse angle from the base (FIG. 5). The thusangled side walls 47 follow corresponding curved portions of the spliceclosure housing 31 and, therefore, provide an enlarged slack storagecapacity for storing slack cable 50 within the slack storage tray 45. Aupper side wall portion 48 of the slack storage tray 45 extends upwardlyat a right angle to the base 45 similar to a conventional slack storagetray. The slack storage tray 45 also includes three tabs 49 extendinginwardly in a plane parallel to the base 46 to thereby facilitatepositioning of the slack 50 within the slack storage tray 45. Asillustrated in FIGS. 4 and 5, tie wraps 51 may be used to secure theslack 50 within the slack storage tray 45.

The cable termination means of the present invention also includes guidemeans 55 positioned within the slack fiber storage tray 45 and to whichthe fiber optic cables 33 are secured (FIG. 4). the guide means 55 mayaccommodate optical fiber ribbon, individual optical fibers, orindividual optical fibers broken out from optical fiber ribbons.

The guide means 55 includes a base 56 and an arcuately shaped wall 57extending upwardly therefrom and having a predetermined bend radius forguiding predetermined ones of optical fibers, or optical fiber ribbons50 as in the illustrated embodiment, to respective transport tubes 40.The guide means 55 also includes a first tab 61 extending outwardlygenerally parallel to the base 56 and a pair of upwardly extending tabs62 spaced apart from the arcuately shaped wall 57 and carried in spacedapart relation therefrom by respective extended portions of the base 56(FIG. 4).

The guide means 55 also includes transport tube retaining means 65including a series of spaced apart walls 66 extending outwardly from thebase 56 of the guide means 55. The spaced apart walls 66 may preferablyhave a serpentine shape to thereby define a series of notches therealongto retain respective transport tubes 40 as best illustrated by thegreatly enlarged view of FIG. 6. The transport tube retaining means 65also includes an enlarged fan-out area 67 immediately prior to theseries of serpentine spaced apart walls 66 to facilitate feeding theoptical fiber ribbons 50 to respective transport tubes 40.

An important feature of the present invention is that the fiber optictransport tube 40 has a differential flexibility to thereby readilyprotect optical fiber ribbons 50 carried within the transport tube frombending in a direction normal to their minor dimension. Such bendingwould likely cause the ribbon to buckle and highly stress the opticalfibers. As shown in the greatly enlarged view of FIG. 7, a preferredcross-sectional shape for the transport tube 40 is generally oval orracetrack-like. As would be readily understood by those skilled in theart, other cross-sectional shapes may also be used to impartdifferential flexibility to the transport tube 40.

The transport tube 40 also preferably has opposing end wall portions 40athat have a predetermined thickness greater than the thickness of theopposing side wall portions 40b. Typical wall thicknesses for apolyethylene transport tube 40 are 0.037" for the end wall portions 40aand 0.032" for the side wall portions 40b. The difference in wallthicknesses is sufficient to impart the desired differential flexibilityto the transport tube 40, yet sufficiently close to permit the transporttube to be readily cut using a conventional ring cutter tool, as wouldbe appreciated by those skilled in the art. The interior majorcross-sectional dimension of the transport tube 40 is preferablyselected to accommodate a typical optical fiber ribbon within the majorinterior dimension as shown in FIGS. 20a and 20b.

The minor interior dimension of the transport tube 40 is preferablyselected to frictionally engage a conventional loose buffer tube 52 withindividual optical fibers 53 therein. Conventional fiber optic buffertubes 52 are available in outside diameters of 0.095"., 0.103", and0.120", all of which may be readily accommodated by the transport tube40 having an minor interior dimension slightly less that 0.095". Such aminor dimension will also accommodate one or several optical fiberribbons 50 so as to restrict the ribbons from unintended rotationalmovement. Thus, the ribbons are maintained within the transport tube 40with their major dimension properly aligned with the major interiordimension of the transport tube. Accordingly, the transport tube 40 ofthe present invention may be advantageously used with either ribbon-typefiber optic cables or with loose tube fiber optic cables as would bereadily appreciated by those skilled in the art.

Referring now to FIGS. 8-12, the features and advantages of the spliceholder 36 according to the invention will now be explained. As would bereadily understood by those skilled in the art, a conventional spliceholder typically secures several splices in side-by-side relation. Thesplice holder must securely hold the splices and prevent damage theretosuch as caused by mechanical shock and vibration. The splice holder 36according to the invention accommodates a variety of differentmanufacturers' splices 70 with different external dimensions. Inaddition, the splice holder 36 protects the splices 70 from shock andvibration.

The splice holder 36 includes a generally rigid shell 71 having apredetermined pattern of openings 73 in a base portion 72 of the shell.The shell 71 also includes a pair of opposing spaced apart side walls74. A pair of flexible inserts 77 is positioned in the shell 71 so thata series of spaced apart walls 78, extending outwardly from a base 80 ofthe inserts 77, passes through the corresponding openings 73 in the baseportion 72 of the shell 71. The walls 78, 78a and the base 80 of theinserts 77 of the illustrated embodiment are integrally molded of aflexible rubber material. Accordingly, the generally rigid shell 71serves to support and stabilize the flexible inserts 77 on a splice tray35.

The flexible walls 78, 78a of the inserts 77 define a series of channels79 for receiving therein respective optical fiber splices 70. As shownin the illustrated embodiment, the outermost walls 78a of the inserts 77at the peripheral opposing sides of the base 80 are solid walls of abouthalf the thickness of the interior walls 78. The side walls 74 of theshell 71 serve to prevent the outermost walls 78a from bowing outwardlyan undesired amount when splices are positioned in the channels 79adjacent the outermost walls 78a.

The flexible inserts 77 according to the invention are preferably formedof injection moldable rubber, that is, non-crosslinked, non-vulcanizedrubber as would be readily known to those skilled in the art. Theinjection moldable rubber permits the inserts 77 to be readily injectionmolded and then subsequently removed from the mold despite theoverhanging projections 82 on the tops of flexible walls 78, 78a. Theprojections 82 further serve to secure different sized splices 70 in therespective channels 79.

As shown best in the bottom view of FIG. 10 and the cross-sectionalviews of FIGS. 11 and 12, each of the flexible walls 78 of the inserts77 includes a hollow cavity 84 extending through a substantial portionthereof vertically from the base 80 to near the top of the wall 78. Thehollow cavity 84 permits a wider range of sizes of splices 70 to bepositioned within the channels 79 and also provides enhanced cushioningand shock absorbing for the splices, especially as compared to a solidwall of a resilient material, for example.

Another aspect of the splice closure 30 according to the presentinvention is the provision of hinge means, including detent means, toreleasably lock individual ones of the splice trays 35 in either of tworaised positions as illustrated in FIGS. 13-18. Accordingly, anunderlying splice tray 35 may be accessed. In prior art splice closures,such as the Raychem model FOSC 100, a freely pivotal splice tray couldbe propped into a raised position by a clip which was inserted adjacentthe pivot point of the tray. The present invention obviates the need forthis separate clip.

A hinge pin 90 is connected at one end of the splice tray 35 by a hingepin mounting bracket 91. The splice tray mounting bracket 37 includes aseries of slotted openings 93 for receiving the hinge pins 90. Moreparticularly, the mounting bracket 37 includes a series of cammedsurfaces 95 including predetermined detent portions 95a, 95b and 95cwhich serve together with the detent bar 96 of the splice tray toreleasably lock the splice tray 35 in a stacked position (FIG. 14), afirst raised position (FIG. 15), and a second raised position (FIG. 16),respectively. The detent bar 96 is secured to the hinge pin mountingbracket 91 in spaced relation from the hinge pin 90.

Another feature of the hinge means is that a splice tray 35 may beremoved from the bracket 37 by aligning the tray in a full uprightposition (FIG. 18) which aligns opposing flat surfaces of the hinge pin90 with the slotted opening 93 to permit the tray to be withdrawn.

FIG. 17 illustrates securing an end of a transport tube 40 to the splicetray 35. An integrally molded wedge 100 is provided in the cornerbetween the side wall 35b and the base 35a of the tray and is secured inposition with a tie wrap 101. Accordingly, the transport tube 40 isaligned at about a 45° angle in the corner so that the tie wrap 101engages the transport tube thereby directing the compressive force ofthe tie wrap against the shorter and slightly thicker end walls 40arather than the longer and slightly thinner side walls 40b of thetransport tube.

As again highlighted by the pivotal motion of the splice trays 35 asillustrated in FIGS. 13-17, it is important that the transport tube 40protect the optical fibers during any such movement. As described above,the transport tube 40 according to the present invention is particularlysuited for protecting optical fiber ribbons, but may also be used forloose buffered fibers as well.

As would be readily understood by those skilled in the art in view ofthe above description relating to the transport tube above, a methodaspect according to the present invention is for protecting an opticalfiber ribbon against undesired bending in a splice closure. The methodincludes the step of positioning over the optical fiber ribbon agenerally flexible transport tube with differential flexibility asdescribed above. Preferably each end of the transport tube is alsosecured, one end to a splice tray and the opposite end to cabletermination means.

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is to be understood that the invention is not to belimited to the specific embodiments disclosed, and that modificationsand embodiments are intended to be included within the scope of theappended claims.

That which is claimed is:
 1. A fiber optic splice closure comprising:a housing; cable termination means connected to said housing for securing one or more fiber optic cables thereto; a bracket connected to said housing; a plurality of splice trays positioned within said housing, each splice tray having an end pivotally connected to said bracket and movable between a stacked position and a raised position to thereby facilitate access to an underlying splice tray; and a plurality of generally flexible transport tubes extending from said cable termination means to said splice trays for carrying optical fibers from one or more fiber optic cables to respective splice trays, each of said transport tubes having a longitudinal axis and including means for imparting to said transport tube differential flexibility between first and second directions transverse to the longitudinal axis.
 2. A fiber optic splice closure according to claim 1 wherein said means for imparting differential flexibility to each of said transport tubes comprises a predetermined cross-sectional shape therefor.
 3. A fiber optic splice closure according to claim 1 wherein said means for imparting differential flexibility to each of said transport tubes comprises a generally oval cross-sectional shape therefor, and wherein said generally oval cross-sectional shape has a predetermined major dimension and a predetermined minor dimension to thereby impart greater flexibility for bending in the direction generally normal to the major dimension of each transport tube.
 4. A fiber optic splice closure according to claim 3 wherein said oval cross-sectional shape of each of said transport tubes has opposing end wall portions and opposing side wall portions, and wherein said opposing end wall portions have a predetermined thickness greater than a predetermined thickness of said opposing side wall portions.
 5. A fiber optic splice closure according to claim 3 wherein said oval cross-sectional shape of each of said transport tubes has a predetermined major interior dimension for receiving therein a fiber optic ribbon comprising a predetermined number of optical fibers arranged in side-by-side relation.
 6. A fiber optic splice closure according to claim 3 wherein said oval cross-sectional shape of each of said transport tubes has a predetermined minor interior dimension for frictionally engaging therein a fiber optic loose buffer tube having an outside diameter within a predetermined range.
 7. A fiber-optic splice closure according to claim 3 wherein each of said splice trays comprises a generally rectangular base and a pair of opposing side walls extending outwardly from said base for retaining slack portions of optical fibers adjacent thereto, and further comprising a wedge positioned in a corner formed by one of said side walls and said base for receiving thereagainst a side wall portion of one of said oval shaped transport tubes.
 8. A fiber optic splice closure according to claim 1 further comprising hinge means for pivotally connecting each of said splice trays to said bracket, and wherein said hinge means includes detent means for releaseably locking a respective splice tray in the raised position.
 9. A fiber optic splice closure according to claim 1 wherein said cable termination means includes guide means for guiding optical fibers from one or more optical fiber cables along a predetermined bend radius and to said transport tubes.
 10. A fiber optic splice closure according to claim 9 wherein said guide means includes a base connected to said bracket and an arcuately shaped wall having the predetermined bend radius and extending outwardly from said base.
 11. A fiber optic splice closure according to claim 10 wherein said guide means includes transport tube receiving means comprising a series of spaced apart walls extending outwardly from said base thereby defining a series of slots receiving therein said transport tubes.
 12. A fiber optic splice closure according to claim 1 wherein said housing is generally cylindrical in shape.
 13. A fiber optic splice closure according to claim 12 further comprising a slack storage tray positioned within said cylindrical housing, and wherein said slack storage tray includes a generally rectangular base and a pair of opposing side walls extending outwardly from said base at a predetermined obtuse angle generally following an adjacent curved portion of said cylindrical housing to thereby provide enlarged slack storage capacity for said slack storage tray.
 14. A fiber optic splice closure according to claim 1 further comprising at least one splice holder positioned on each of said splice trays for securing thereto a plurality of optical fiber splices in side-by-side relation.
 15. A fiber optic splice closure according to claim 14 wherein said at least one splice holder comprises:a base; and a series of spaced apart flexible walls extending outwardly from said base and defining a series of channels between adjacent pairs of said walls, each of said walls having a hollow cavity extending through a substantial portion thereof and being formed of a flexible material to thereby readily accommodate splices of different sizes within respective channels.
 16. A fiber optic splice closure according to claim 15 wherein said base and said walls of said at least one splice holder are formed of integrally molded rubber.
 17. A fiber optic splice closure according to claim 16 further comprising a rigid shell overlying said base of said at least one splice holder and having a predetermined pattern of openings therein corresponding to said series of spaced apart walls and through which said walls extend.
 18. A fiber optic splice closure according to claim 1 wherein said housing includes an end cap, wherein said bracket is generally U-shaped, and wherein a leg of said U-shaped bracket is secured to said end cap thereby permitting one or more fiber optic cables to be routed through an opening of said U-shaped bracket to an opposite side of said housing.
 19. A fiber optic splice closure according to claim 1 wherein each of said splice trays comprises a generally rectangular base and a pair of opposing side walls extending outwardly from said base for retaining slack portions of optical fibers adjacent thereto, and further comprising at least one pair of spaced apart ridges on an inner portion of each of said opposing side walls of said tray so as to permit insertion of a hooked probe between said ridges to thereby facilitate separation of a predetermined optical fiber or group of optical fibers from adjacent slack optical fibers.
 20. A fiber optic splice closure comprising:a housing; cable termination means connected to said housing for securing one or more fiber optic cables thereto; a splice tray positioned within said housing; and at least one generally flexible transport tube extending from said cable termination means to said splice tray for carrying optical fibers from one or more fiber optic cables to said splice tray, said at least one transport tube having a longitudinal axis and including means for imparting to said transport tube differential flexibility between first and second directions transverse to the longitudinal axis.
 21. A fiber optic splice closure according to claim 20 wherein said means for imparting differential flexibility to said at least one transport tube comprises a predetermined cross-sectional shape therefor.
 22. A fiber optic splice closure according to claim 20 wherein said means for imparting differential flexibility to said at least one transport tube comprises a generally oval cross-sectional shape therefor, and wherein said generally oval cross-sectional shape has a predetermined major dimension and a predetermined minor dimension to thereby impart greater flexibility for bending in the direction normal to the major dimension of said at least one transport tube.
 23. A fiber optic splice closure according to claim 22 wherein said oval cross-sectional shape of said at least one transport tube has opposing minor dimension end wall portions and opposing major dimension side wall portions, and wherein said opposing minor dimension end wall portions have a predetermined thickness greater than a predetermined thickness of said opposing major dimension side wall portions.
 24. A fiber optic splice closure according to claim 22 wherein said oval cross-sectional shape of said at least one transport tube has a predetermined major interior dimension for receiving therein a fiber optic ribbon comprising a predetermined number of optical fibers arranged in side-by-side relation.
 25. A fiber optic splice closure according to claim 22 wherein said oval cross-sectional shape of said at least one transport tube has a predetermined minor interior dimension for frictionally engaging therein a fiber optic loose buffer tube having an outside diameter within a predetermined range.
 26. A fiber-optic splice closure according to claim 22 wherein said splice tray comprises a generally rectangular base and a pair of opposing side walls extending outwardly from said base for retaining slack portions of optical fibers adjacent thereto, and further comprising a wedge positioned in a corner formed by one of said side walls and said base for receiving thereagainst a side wall portion of one of said oval shaped transport tubes.
 27. A fiber optic splice closure according to claim 20 wherein said housing is generally cylindrical in shape.
 28. A fiber optic splice closure according to claim 27 further comprising a slack storage tray positioned within said cylindrical housing, and wherein said slack storage tray comprises a generally rectangular base and a pair of opposing side walls extending outwardly from said base at a predetermined obtuse angle generally following an adjacent curved portion of said cylindrical housing to thereby provide greater slack storage capacity for said slack storage tray.
 29. A fiber optic splice closure according to claim 20 further comprising at least one splice holder positioned on said splice tray for securing thereto a plurality of optical fiber splices in side-by-side relation.
 30. A fiber optic splice closure according to claim 29 wherein said at least one splice holder comprises:a base; and a series of spaced apart flexible walls extending outwardly from said base and defining a series of channels between adjacent pairs of said walls, each of said walls having a hollow cavity extending through a substantial portion thereof and being formed of a flexible material to thereby readily accommodate splices of different sizes within respective channels.
 31. A fiber optic splice closure according to claim 30 wherein said base and said walls of said at least one splice holder are formed of integrally molded rubber.
 32. A fiber optic splice closure according to claim 31 further comprising a rigid shell overlying said base of said at least one splice holder and having a predetermined pattern of openings therein corresponding to said series of spaced apart walls and through which said walls extend.
 33. A fiber optic splice closure according to claim 20 wherein said splice tray comprises a generally rectangular base and a pair of opposing side walls extending outwardly from said base for retaining slack portions of optical fibers, and further comprising at least one pair of spaced apart ridges on an inner portion of each of said opposing side walls of said tray to permit insertion of a hooked probe between said ridges to thereby facilitate separation of a predetermined optical fiber or group of optical fibers from adjacent slack optical fibers.
 34. A fiber optic splice closure comprising: a housing;cable termination means connected to said housing for securing one or more fiber optic cables thereto: a splice tray positioned within said housing separately from said cable termination means; and at least one generally flexible transport tube extending from said cable termination means to said splice tray for carrying optical fibers from one or more fiber optic cables to said splice tray; said cable termination means including guide means for guiding optical fibers from one or more optical fiber cables along a predetermined bend radius to said at least one transport tube, said guide means including transport tube receiving means having a fiber fan-out area immediately prior thereto.
 35. A fiber optic splice closure according to claim 34 wherein said guide means includes a base operatively connected to said housing and an arcuately shaped wall having the predetermined bend radius and extending outwardly from said base.
 36. A fiber optic splice closure according to claim 35 wherein said transport tube receiving means comprises a series of spaced apart walls extending outwardly from said base defining a series of slots receiving therein said at least one transport tube.
 37. A fiber optic splice closure according to claim 34 wherein said at least one transport tube has a longitudinal axis and has a predetermined cross-sectional shape for imparting to said transport tube differential flexibility between first and second directions transverse to the longitudinal axis.
 38. A fiber optic splice closure according to claim 37 wherein the predetermined cross-sectional shape of said at least one transport tube is generally oval, and wherein said oval cross-sectional shape has a major dimension and a minor dimension to thereby impart greater flexibility for bending in the direction normal to the major dimension of said at least one transport tube.
 39. A fiber optic splice closure according to claim 38 wherein said oval cross-sectional shape of said at least one transport tube has opposing end wall portions and opposing side wall portions, and wherein said opposing end wall portions have a predetermined thickness greater than a predetermined thickness of said opposing side wall portions.
 40. A fiber optic splice closure according to claim 38 wherein said oval cross-sectional shape of said at least one transport tube has a predetermined major interior dimension for receiving therein a fiber optic ribbon comprising a predetermined number of optical fibers arranged in side-by-side relation.
 41. A fiber optic splice closure according to claim 38 wherein said oval cross-sectional shape of said at least one transport tube has a predetermined minor interior dimension for frictionally engaging therein a fiber optic loose buffer tube having an outside diameter within a predetermined range.
 42. A fiber optic splice closure according to claim 34 further comprising at least one splice holder positioned on said splice tray for securing thereto a plurality of optical fiber splices in side-by-side relation.
 43. A fiber optic splice closure according to claim 42 wherein said at least one splice holder comprises:a base; and a series of spaced apart flexible walls extending outwardly from said base and defining a series of channels between adjacent pairs of said walls, each of said walls having a hollow cavity extending through a substantial portion thereof and being formed of a flexible material to thereby readily accommodate splices of different sizes within respective channels.
 44. A fiber optic splice closure according to claim 43 wherein said base and said walls of said at least one splice holder are formed of integrally molded rubber.
 45. A fiber optic splice closure according to claim 43 further comprising a rigid shell overlying said base of said at least one splice holder and having a predetermined pattern of openings therein corresponding to said series of spaced apart walls and through which said walls extend.
 46. A fiber optic splice holder comprising: a base;a series of spaced apart flexible walls extending outwardly from said base and defining a series of channels between adjacent pairs of said walls, each of said walls having a hollow cavity extending through a substantial portion thereof and being formed on a flexible material to thereby readily accommodate splices of different sizes within respective channels, and a rigid shell overlying said base and having a predetermined pattern of openings therein corresponding to said series of spaced apart walls and through which said walls extend.
 47. A fiber optic splice holder according to claim 46 wherein said base and said walls are formed of integrally molded rubber.
 48. A fiber optic splice holder according to claim 46 further comprising a pair of opposing solid flexible side walls extending outwardly from said base at peripheral opposing sides of said series of spaced apart walls.
 49. A fiber optic splice holder according to claim 48 wherein said shell further comprises a pair of opposing generally rigid side walls adjacent an outer portion of said pair of opposing solid flexible side walls so as to substantially prevent outward flexing thereof.
 50. A fiber optic splice holder comprising:a pair of inserts arranged in spaced apart relation, each insert comprising a flexible base, and a series of spaced apart flexible walls extending outwardly from said base and integrally molded therewith, said series of spaced apart walls defining a series of channels between adjacent pairs of said walls, each of said walls being formed of a flexible material to thereby readily accommodate splices of different sizes within respective channels; and a rigid shell overlying both of said bases of said pair of inserts and having a predetermined pattern of openings therein corresponding to said series of spaced apart walls and through which said walls extend.
 51. A fiber optic splice holder according to claim 50 wherein each of said walls of said pair of inserts has a hollow cavity extending through a substantial portion thereof.
 52. A fiber optic splice holder according to claim 50 wherein each of said inserts further comprises a pair of opposing solid flexible side walls extending outwardly from said flexible base at peripheral opposing sides of said series of spaced apart walls, and wherein said pair of side walls is integrally molded with said flexible base.
 53. A fiber optic splice holder according to claim 52 wherein said shell further comprises a pair of opposing generally rigid side walls adjacent an outer portion of said pair of opposing solid flexible side walls of said pair of inserts so as to substantially prevent outward flexing thereof. 